N. Marigheto

Thermally induced structural changes in glycinin, the 11S globulin of soya bean (Glycine max)—an in situ spectroscopic study

The thermal denaturation behaviour of glycinin solutions has been studied in situ as a function of ionic strength using various spectroscopic methods. Changes in secondary structure occurred at temperatures above 60 degrees C, well before the onset of gelation. Even after heating to 95 degrees C, much of the native beta-sheet structure of glycinin was retained, as indicated by the amide I peak maximum at 1635 cm(-1) in the Fourier transformed infrared (FT-IR) spectrum. This was accompanied by an increase in the 1625 cm(-1) band, indicative of the formation of intermolecular beta-sheet associated with protein aggregation. Nuclear magnetic resonance (NMR) spectroscopy confirmed the presence of highly mobile regions in glycinin comprising predominantly of Gln and Glu residues, corresponding to mobile regions previously identified by crystallographic studies. There was also evidence of a hydrogen-bonded structure within this mobile region, which may correspond to an alpha-helical region from Pro(256) to (or just before) Pro(269) in proglycinin. This structure disappeared at 95 degrees C, when heat-set gel formation occurred, as indicated by a sudden broadening and weakening of the NMR signal. Otherwise the NMR spectrum changed little during heating, emphasising the remarkable thermal stability of glycinin. It is proposed that during heating the core beta-barrel structure remains intact, but that the interface between the beta-domains melts, revealing hydrophobic faces which may then form new structures in a gel-network. As Cys(45), which forms the disulfide with Cys(12) linking the acidic and basic polypeptides, is found in this interface, such a rearrangement of the individual beta-domains could be accompanied by cleavage of this disulfide bond, as is observed experimentally. Such information contributes to our understanding the aggregative behaviour of proteins, and hence develops knowledge-based strategies for controlling and manipulating it.

T1−T2 NMR correlation studies of high-pressure-processed starch and potato tissue

Two-dimensionalT1−T2 correlation spectroscopy is used to monitor the effect of high-pressure and microwave processing on the microscopic water distribution and starch chain dynamics in water-saturated packed beds of native A and B type starches. B type starches are shown to be more resistant to pressure treatment than A type starches. High-pressure-induced A type starch gels are also shown to be radically different from the corresponding thermally induced gel. Although the cell walls of raw potato are resistant to high-pressure damage, the tonoplast and plasmalemma membranes are disrupted by high pressure.

Geographical origin differentiation of saffron spice (Crocus sativus L. stigmas) - Preliminary investigation using chemical and multi-element (H, C, N) stable isotope analysis.

A preliminary study of the bulk hydrogen, carbon and nitrogen stable isotope composition of 28 authentic saffron samples produced from Crocus sativus L. cultivated in the typical production areas of Western Macedonia in Greece (8), Khorasan Province in Iran (7), Sardinia in Italy (6) and Castilla-La Mancha in Spain (7) is described. A chemical characterisation of 16 key quality parameters was also completed on the same samples by UV-Vis, HPLC and GC analyses. Multivariate analysis of the data revealed that 60.7% of saffron samples could be correctly assigned to their respective production countries using the chemical parameters. However, the combined bio-element stable isotope data reliably classified 100% of the saffron samples according to their respective geographical origins using posterior cross validation. Further work is required to establish the long-term stability of these models with respect to different years of production and other major producers such as India and Morocco.

Sr isotope measurements in beef: analytical challenge and first results

AbstractThe strontium isotope ratio (87Sr/86Sr) in beef, derived from 206 European cattle, has been measured. These cattle were located in 12 different European regions within France, Germany, Greece, Ireland, Italy, Spain and the UK. As animal protein is known to be a difficult material on which to conduct Sr isotope analysis, several investigations were undertaken to develop and improve the sample preparation procedure. For example, Sr isotope analysis was performed directly on freeze-dried meat and defatted dry mass from the same samples. It was found that enormous differences—sometimes exceeding the measurement uncertainty—could occur between the fractions and also within one sample even if treated in the same manner. These variations cannot be definitely allocated to one cause but are most likely due to inhomogeneities caused by physiological and biochemical processes in the animals as post mortem contamination during analytical processing could be excluded. For further Sr isotope measurements in meat, careful data handling is recommended, and for the authentic beef samples within this project, it was decided to use only freeze-dried material. It can be demonstrated, however, that Sr isotope measurements in beef proteins are a valuable tool for authentication of geographic origin. Although partly overlapping, some of the European sampling sites could be discriminated even by only using 87Sr/86Sr. FigureBox plot diagram displaying 87Sr/86Sr in authentic beef samples ordered by Trace sampling sites

NMR protocol for on-line Brix determination

Water suppression by diffusive attenuation was used to measure Brix in intact cellular tissue of apple and strawberry. Given the signal-to-noise ratio, the correlation for apple was established without repeated acquisition, so this protocol should also be useful for rapid, on-line measurements at low spectrometer frequencies. Water suppression by theT1-Null method fails with cellular tissue because of the considerable variation in the longitudinal relaxation times of vacuolar and cytoplasmic water.

Preliminary Investigation into the Geographical Origin Differentiation of Saffron (Crocus sativus L.) by Multi-Element (HCN) Stable Isotope Analysis

A simple solvent extraction was performed to remove the majority of the lipid in saffron and eliminate any variability in isotopic composition due to variable lipid content. The global hydrogen, carbon and nitrogen (HCN) stable isotope composition of the defatted dry mass fraction was measured by elemental analyses and high temperature conversion coupled to an Isotope Ratio Mass Spectrometer. The objective of this study was to differentiate the geographical origin of saffron coming from different countries (Greece, Italy, Iran and Spain) by measuring the stable isotopic composition of the bio-elements hydrogen, carbon and nitrogen. Also a chemical characterization of 28 saffron samples was carried out by UV-Vis, HPLC and GC analysis.